1. Field of the Invention
The present invention relates to a process for regenerating a permanganate and/or a manganate from manganese dioxide discharged from the process for removing NO.sub.x by using the permanganate and/or the manganate.
2. Description of the Prior Art
In a process for absorbing NO.sub.x in an exhaust gas into an alkaline aqueous solution of a manganese oxoacid salt such as potassium permanganate or potassium manganate, the manganese compounds are included in the discharged wastes which causes pollution.
The inventors have studied and proposed to prevent the precipitation of manganese dioxide in a chemical reaction, however it has not been succeeded to prevent the discharge of manganese (VII) (VI) compounds which are discharged with the resulting nitrate and nitrite.
Heretofore, the manganese (VII) (VI) compounds have been reduced to manganese dioxide in pH of about 8, and the precipitated manganese dioxide has been separated and it has been oxidized from Mn.sup.+4 to Mn.sup.+6 by an alkali fusion and it has been further oxidized from Mn.sup.+6 to Mn.sup.+7 by an electrolytic oxidation to attain the regeneration. The process has not been economical to combine it in a line of processes for treating the exhaust gas from the viewpoints of the apparatus and the running cost.